Printed circuit boards (PCB) have long been used as the base for sophisticated electronic systems. An electrically insulating sheet, originally phenolic impregnated fabrics and now generally fiberglass reinforced resins, is coated with copper cladding and has appropriate patterns etched into the cladding. In years past, most electronic components had wire leads that extended through holes drilled into the cladding pattern and filled with solder to make the required connections. More recently, surface bonding of relatively short leads to the cladding has become common, allowing for thigh speed robotic placement of components.
Today, electronic devices are increasing miniaturized and it has become desirable to mount component on both sides of a PCB. However, there are a number of problems in installing parts on the second side after components have been mounted on the first side. The board cannot be held flat with downwardly projecting components of various sizes and thicknesses mounted on the lower side. This problem is most acute when solder paste is to be printed on the second side. Holding the PCB flat and level under a paste application stencil during solder paste application and then during component placement is very difficult.
In high production run circumstances, aluminum plates or similar material have been machined out in a pattern corresponding to the topography of the first side of the PCB with components installed. This approach is not practical for manufactures or subcontractor producing a limited quantity of a very great number of PCB configurations, each requiring its own "hogged-out" support plate.
Supports have also been made by casting a plaster like material into a mold corresponding to a particular PCB to form a support having pockets for receiving the components on the downwardly extending board side.
While effective where a large number of identical boards are to be manufactured, these methods are not cost effective where only a few boards are to be made or where custom boards are being manufactured.
A number of different devices having a plurality of adjustable length upstanding fingers have been developed to support irregularly shaped article. Typical of these is the device for supporting parts during machining as described by Barozzi in U.S. Pat. No. 4,936,560, the casting support device describe by Godding in U.S. Pat. No. 4,200,272, and the core support system described by Bourassa et al. in the U.S. Pat. No. 3,530,994.
While these supports are generally effective for their intended purposes, they are overly complex, and do not always provide positive support across the supported object.
A circuit board support system using a plurality of space, parallel, upwardly extending piston is described by Fadiga et al. in U.S. Pat. No. 3,942,778. This support is used to press the back of the boards against test sensors. Since the pistons are not lockable to match a particular PCB, each succeeding board must be pressed down against the positions, risking damage. Further, the system is not readily useful in installing components on the back of the board, since the pistons continue to press upwardly so that the board may not lie truly flat and may move during back side component installation.
Thus, there is a continuing need for improved supports for holding a substrate such as a printed circuit board having components mounted on one side while additional components are installed on the opposite side, that will support the board in a precisely level position, that will provide strong, consistent support for the board during second surface Stencil printing and soldering operations, that can easily be locked in the support position appropriate to a series of similarly configured boards, that precisely indexes board edges and that is easily unlocked and reconfigured for other boards.